Vector control is a common technique used in the control of high performance motor drives. The principle of vector control relies on orientation of the synchronous reference frame with one of the fluxes of the machine (either stator or rotor flux). Proper control and torque production of the machine relies on accurate alignment of the synchronous reference frame to the desired motor flux, such as accurate alignment with the rotor magnet north pole. Incorrect alignment will result in erroneous torque production, and possible instability of current control. It is therefore imperative that an accurate and reliable method of rotor alignment be selected.
If a mechanical position sensing device is employed, such as a resolver, the device can be aligned at the factory to the rotor magnet north pole. However, some systems do not employ a position sensing device. Rather, a position sensorless control algorithm is used to estimate the rotor position based upon machine quantities such as currents and voltages. Many such position sensorless control techniques exist, and most are based upon detecting the saliency of the motor. The saliency of the motor is the variation of spatial inductance of the motor around the circumference of the airgap. For example, in an interior permanent magnet (IPM) motor, the rotor magnets are buried in the rotor. This results in different D and Q axis inductances (or saliency). While conventional techniques exist to detect this saliency, and hence provide rotor position information, these prior art techniques typically cannot differentiate between the positive and negative D axis (i.e., the rotor magnet north and south poles). Typically, a second technique is employed to resolve the proper alignment with the north pole once the positive or negative D axis has been identified. These typical techniques, however, generally involve significant computations and/or considerable time.
Accordingly, it is desirable to provide a method and apparatus for simply and reliably resolving the rotor magnet pole orientation. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.